Product availability by State or Zone

[greenview]

We had customized our current version of AbleCommerce (5.5) to allow us to restrict shipping to certain states, as some of our products are only registered for sale in specific states and regions. In migrating to this or the latest AbleCommerce version, is this something that can be easily managed using "Zones" or should we count on porting our customization over to the newer version? We don't want the user to wait necessarily until they reach checkout to find the product is not shippable -- our current web site allows shoppers to enter their zip code to determine product availability, and if the product is not registered for sale to that state, we provide them a link to find a local store instead. As I mentioned, we have added a lot of customizations to the source, which does hinder our migration path, so I'd like to minimize the number of customizations that we have to re-implement.